Last week, Stephen Sondheim e-mailed me to say that his letters to his collaborator Arthur Laurents are available to anyone who “cares enough to go down to the Library of Congress to read them.”

Laurents, as I reported, left all his papers to the library with unrestricted access.

But I’m afraid Sondheim was being disingenuous. I checked with the library and was told that his letters are “momentarily sealed.” They can be viewed only with his permission.

But if they’re not readily available at the Library of Congress, I have easy access to them at the Library of Riedel.

On we go!

Sondheim enjoyed dish so much, he crafted a Jan. 25, 1968, letter in the style of a newspaper gossip column. He even bulleted his items.

The juiciest entry is his assessment of Barbra Streisand’s performance at a Broadway for Peace Benefit. (This was at the height of the Vietnam War.)

Streisand sang a song called “So Pretty” by Leonard Bernstein, Betty Comden and Adolph Green. Sondheim didn’t think much of the number. He told Laurents it would likely prolong the war for years.

But he saved most of his venom for Streisand’s appearance and performance.

He was convinced she was wearing a wig, though David Shire, who conducted for her, assured him the ringlets she sported did in fact sprout from her head.

Sondheim was appalled at how much weight she’d put on, saying her tight-fitting sequin dress and growing number of chins made her look like a Red Hot Mama from the 1920s.

As for her performance, he complained it was devoid of genuine feeling, calling it a cynical exercise from a self-centered movie star who didn’t give a damn about her audience anymore.

Another chance to disapprove, another brilliant zinger!

Streisand, by the way, had her own take on her fast-moving career. Laurents directed her in “I Can Get It for You Wholesale,” the 1962 musical that marked her Broadway debut. They became good friends. But after he criticized her first record, “The Barbra Streisand Album” (1963), she wrote back defending herself against the charge that she acted as though she were already a big star.

She noted that ever since she was 6 years old, people accused her of being snooty. She said she could never behave like a star because she lacked confidence.

(She certainly got over that!)

She said she was dismayed because now that she was getting national attention, her old friends were turning on her. They were envious, she said, of her success.

Though she was hurt by Laurents’ letter, she still valued his advice and hoped he would write something for her to perform in upcoming appearances in London and New York.

Streisand wasn’t the only performer to undergo a flogging in Sondheim’s letter of ’68.

In another item, he reported on the closing night of “Hallelujah, Baby!” — which Laurents wrote and directed. He liked the show but savaged its star, Leslie Uggams, for mangling the lyrics, stepping out of character, basking in audience adoration and acting like a narcissistic diva.

An actor! It’s compacter! And always arrives overdone . . .

Coming soon: Steve and Arthur at each other’s throats over “Anyone Can Whistle.”